1. Field of the Invention
This invention relates to tongs for making and breaking joints between adjacent threaded members and, in particular, to tongs having a sensing unit in a force-receiving relationship with respect thereto for generating a signal functionally related to the magnitude of the actuating force applied to the tongs.
2. Description of the Prior Art
In the hydrocarbon industry it is common practice to interengage threaded members in order to provide extended strings of drill pipe, production tubing, well casing, or wash pipe (depending upon the particular application). These interconnected strings of members may extend for several miles beneath the surface of the earth. In other instances it is often necessary to interengage relatively shorter assemblages of elements, for example, the engagement of sucker rods or the like or the assembly of a bottom hole survey apparatus.
The apparatus utilized to provide the torque necessary to assemble and disassemble ("make-up" or "break-out", respectively) the assembly of elements is known as a tongs. The tongs is a specific type of wrench which typically includes a set of jaws containing dies for grippingly engaging the exterior diameter of one adjacent member. The other member is held stationary with respect to the first member and an actuating force is applied to a tongs handle so that the necessary torque may be applied to the first member to make-up or break-out the threaded interconnection.
Manually operable tongs typically may contain two, three or more pivotally interconnected jaw members which may be closed into gripping engagement about a threaded member in anticipation of the application of a torque thereto. When the application of the force is completed the jaws are opened so as to permit removal of the tongs therefrom. The handle is the moment arm through which the force to effect the make-up or break-out of the threaded joint between the members may be applied. Usually, a chain, catline or the like links the end of the handle with the arrangement for generating the actuating force applied to the tongs. The manually operable tongs are typically suspended from a hanger or handle from suitable guy lines or the like disposed on the drilling installation.
Alternatively, there are arrangements known in the art as power tongs whereby the jaws are disposed in a housing circumferentially encompassing the bore opening and through which protrude the threaded members. This tongs arrangement is typically hydraulically operated and includes a tongs lift arrangement whereby the tongs are raised and lowered to a predetermined operating position about a horizontal datum at which the joint to be made-up or broken-out is located. One set of jaws, (the "back-up" jaws) is then moved radially inwardly into gripping engagement with one of the members while another set of jaws (the "driven" jaws) are moved into gripping engagement with the member which is to be rotated with respect to the first. A hydraulic tongs motor or the like applies the force which is used to effect the make-up or break-out of the joint between the adjacent threaded members.
In the case of both the manual and the power driven tongs it is advantageous to have some indication as to the magnitude of the torque applied to the threaded member. This indication has utility, for example, to prevent the application of excessive torque to the threaded member.
In the power tongs arrangement it is conventional to provide some feedback signal from the hydraulic tongs motor indicative of the amount of hydraulic pressure applied to the driven tongs. In the manually operable tongs a suitable tension meter or the like is affixed in the chain linking the end of the tongs handle to the force generating arrangement and obtaining an indication as to the magnitude of the force applied to the handle.
It will be observed, however, that both of the abovedescribed conventional methods are "indirect" in the sense that they provide an indication of the force applied to the end of the moment arm of the jaws distant from the end of that arm in proximity to the gripping jaws. In the particular instance of the manually operable tongs, the disposition of the sensing unit in the chain linkage may also be subject to errors or imprecision if the chain is not disposed perpendicularly to the axis of the handle. It will be recognized that such angulation provides a misreading of the force applied to the moment arm and any calculation of torque based thereon is commensurately imprecise.
It is believed to be advantageous to provide a tongs arrangement having a sensing unit disposed in a force-receiving relationship with the handle of the tongs (either manually operable or power driven tongs) in order that an indication of the magnitude of the torque applied to the tongs may be more accurately monitored.